Bartosik M, Rumeau C, Hahn R, Zhang Z L, Mayrhofer P H
Institute of Materials Science and Technology, TU Wien, A-1060, Vienna, Austria.
Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, A-8700, Leoben, Austria.
Sci Rep. 2017 Nov 28;7(1):16476. doi: 10.1038/s41598-017-16751-1.
Hard coatings used to protect engineering components from external loads and harsh environments should ideally be strong and tough. Here we study the fracture toughness, K , of TiAlN upon annealing by employing micro-fracture experiments on freestanding films. We found that K increases by about 11% when annealing the samples at 900 °C, because the decomposition of the supersaturated matrix leads to the formation of nanometer-sized domains, precipitation of hexagonal-structured B4 AlN (with their significantly larger specific volume), formation of stacking faults, and nano-twins. In contrast, for TiN, where no decomposition processes and formation of nanometer-sized domains can be initiated by an annealing treatment, the fracture toughness K remains roughly constant when annealed above the film deposition temperature. As the increase in K found for TiAlN upon annealing is within statistical errors, we carried out complementary cube corner nanoindentation experiments, which clearly show reduced (or even impeded) crack formation for annealed TiAlN as compared with their as-deposited counterpart. The ability of TiAlN to maintain and even increase the fracture toughness up to high temperatures in combination with the concomitant age hardening effects and excellent oxidation resistance contributes to the success of this type of coatings.
用于保护工程部件免受外部载荷和恶劣环境影响的硬质涂层理想情况下应兼具高强度和高韧性。在此，我们通过对自支撑薄膜进行微断裂实验，研究了TiAlN退火后的断裂韧性K。我们发现，当在900°C对样品进行退火时，K增加了约11%，这是因为过饱和基体的分解导致了纳米尺寸区域的形成、六方结构B4AlN（其比容显著更大）的析出、堆垛层错的形成以及纳米孪晶。相比之下，对于TiN，由于退火处理无法引发分解过程和纳米尺寸区域的形成，当其在高于薄膜沉积温度下退火时，断裂韧性K大致保持不变。由于TiAlN退火后K的增加在统计误差范围内，我们进行了补充的立方角纳米压痕实验，结果清楚地表明，与沉积态的TiAlN相比，退火后的TiAlN裂纹形成减少（甚至受到阻碍）。TiAlN在高温下保持甚至提高断裂韧性的能力，以及伴随的时效硬化效应和优异的抗氧化性，促成了这类涂层的成功应用。
